1. Field of the Invention
This invention relates to a rubber composition for tires, and more particularly to a rubber composition for tires having improved heat build-up and high temperature reinforcibility.
2. Related Art Statement
Heretofore, various attempts for simultaneously improving the heat built-up and reinforcibility have been made in rubber compositions used in tires and other rubber articles.
For instance, Japanese Patent laid open No. 62-184,463 discloses that the dispersibility of carbon black is improved by restraining the formation of strong acidic group such as --COOH group or the like introduced into the surface of carbon black and preferentially producing --OH group through low temperature plasma treatment, whereby the resistance to heat build-up and the reinforcibility of the rubber composition can be improved.
On the other hand, Japanese Patent laid open No. 50-88,150 discloses that a given amount of at least one of active silicate filler and bis(alkoxysilylalkyl)oligosulfide is used and mixed in a mixture of natural rubber and synthetic rubber together with, if necessary, o.1.about.50 parts by weight of carbon black based on 100 parts by weight of rubber ingredient. Similarly, Japanese Patent laid open No. 61-287,802 discloses a technique for the provision of tires having excellent cut resistance and low heat build-up by using as a base rubber for the tire tread of cap/base structure a rubber composition containing 30.about.50 parts of carbon black having a specific surface area of not less than 100 mg/g as measured by iodine adsorption process, 5.about.30 parts of silica, 0.5.about.6 parts of a silane coupling agent represented by the general formula of (OR).sub. 3SiC.sub.n H.sub. 2nS.sub.m C.sub.n H.sub. 2nSi(OR).sub. 3 or (OR).sub.3 SiC.sub.n H.sub.2 nX (wherein R is an alkyl group, X is a mercapto group, an amino group or an epoxy group, and n and m are a positive integer, respectively) and a given amount of a softening agent based on rubber ingredient composed of natural rubber and styrene-butadiene rubber.
Furthermore, Japanese Patent laid open No. 61-291,659 discloses a modified carbon black having an improved dynamic heat stability by treating a conductive carbon black with a silicon compound in a solvent, and Japanese Patent laid open No. 62-197,429 discloses a composition for a conductive shrinkable film containing (a) 10.about.50 parts by weight of a conductive carbon black and (b) 0.5.about.5 parts by weight of an organic silane coupling agent and/or an imidazole series compound based on 100 parts by weight of polybutadiene.
However, it can be said that these conventional techniques are still insufficient from a viewpoint of simultaneous large improvements of the resistance to heat build-up and the reinforcibility aiming at the invention.
That is, the technique described in Japanese Patent laid open No. 62-18,446 is attempted to simultaneously establish the heat build-up and the reinforcibility of the rubber composition by preferentially producing --OH group on the surface of carbon black to improve the dispersibility of carbon black through low temperature plasma treatment. In this technique, however, the carbon black is insufficient in the interaction with the polymer rubber even at the active state because the surface of the carbon black is modified, and consequently when the rubber composition is used in tires used under severe service conditions, it is particularly insufficient for practical use in view of the high temperature reinforcibility.
On the other hand, the rubber composition described in Japanese Patent laid open No. 50-88,150 and No. 61-287,802 uses silica and silane coupling agent and further reinforcible carbon black, but the chemical bonding between silane coupling agent and carbon black is not sufficiently performed even when being mixed with the silane coupling agent or when modifying carbon black therewith, and consequently the bonding between rubber polymers can not sufficiently be performed through carbon black and silane. As a result, it is not practically regarded to reach to a sufficiently satisfactory level as a rubber composition for tires in view of tensile strength at high temperature and heat buildup. Therefore, these techniques have naturally a limit when they are applied to high performance tire members requiring the high temperature reinforcibility.